I agree that there's a lot we don't know. What were Cooper's intentions/expectations coming in? He was probably expecting to get a sport chute, as in steerable/controllable. Had he planned for another, more known and hospitable landing site? Once he was in the position he was, I agree that he didn't really have a lot of choice but to go. Doing this thing in the first place means he was either ballsy, crazy, or some combination. I still can't completely discount the possibility that he didn't jump over Washington, but somewhere else later, like on the approach to Reno. He could have messed with the stairs to fake out the crew. Once they thought he was gone, how close attention did they pay to other 'bumps' that might have signaled an exit. Flight is a fluid environment, there are a lot of turbulent bumps and dips that occur normally.
As for the jump as it was... I think the odds are greatly in his favor that he gets under an open canopy. The question for me is his landing. If he lands in water, he's got a serious problem. If not, the question is what specific type of terrain did he land in? Does he get injured to the point where he can't hike or crawl out?
Would I do the jump with the gear and in the conditions assumed? At my age today, I seriously doubt it. At 25, maybe to probably. At 45, hard to say, but still maybe.
One thing I've asked and have not seen an answer to is, does anybody know what the moon was that night? As in, how much ambient light was there?